Conventionally, an optical disk which records information or reproduces recorded information using laser light has been practically used. As types of the optical disk, there are a reproduction-only type, a write-once type, and a rewritable type. In the write-once type and the rewritable type, it is necessary that the address information indicating the position of the optical disk be preliminarily recorded for the recording of the information.
As methods to record the address information, two types have been known. One is a format which records the address information as a preformat pit. The other is a format in which a signal that forms a trench referred to as a wobble for the trench is modulated by the address information. In recording the preformat pit, there is a problem that a recording area of user data and a recording capacity of the optical disk decrease. In a wobble format, there is an advantage of not having such a problem. A trench is referred to as a groove, and a track formed by the groove is referred to as a groove track. The groove is defined as a part which is irradiated with laser light when the optical disk is manufactured. An area sandwiched between the adjacent grooves is referred to as a land, and the track formed by the land is referred to as a land track.
When an address is recorded by the wobble, a method (suitably referred to as a land/groove recording format) in which the data is recorded in both the groove track and the land track is desirable, in order to further increase the recording capacity. In the land/groove recording format, the address information for the groove track can be recorded by deflecting the laser light when cutting. However, it is difficult to record the address for the land track by the wobble. When the land track is scanned, the wobbles of the groove track on both sides are reproduced. Furthermore, these wobbles are information of different groove tracks. Therefore, the phases of the wobbles are not aligned, and it is difficult to reproduce the wobbles normally.
Conventionally, in the land/groove recording format, the optical disk, capable of reproducing addresses of both the groove track and the land track, has been proposed. Patent Document 1 describes the disclosure in which the address is intermittently recorded and the phase of the recording position of the address is reversed for the adjacent groove track, when the address is recorded in the groove track by the wobble. As a result of this, the address information originally recorded is intermittently reproduced when a wobble track is reproduced. Then, the addresses of the adjacent groove tracks on both sides are reproduced alternately when the land track is reproduced. Therefore, wobble information (address information) can be obtained in either of groove scanning and land scanning.
Patent Documents 2 and 3 describe the disclosures in which the land track and the groove track are each wobbled, and the address information is recorded by the wobble on a side wall on one side in each track. In addition, an address information block of the wobble track and the address information block of the groove track are arranged by being shifted in a track direction.